As light emitting diodes (LEDs), particularly blue or ultraviolet (UV) LEDs having an emission wavelength of approximately 250 nm to 550 nm, high-brightness products using a compound semiconductor made of a GaN-based compound such as GaN, GaAlN, InGaN or InAlGaN have been developed. Also, it is possible to form a high-definition full-color image using a technique of combining the above-described blue LEDs with red and green LEDs. For example, there is a known technique of manufacturing a white LED by combination of the blue or UV LED with a fluorescent material. Such a white LED is expected to be increasingly used for backlights of liquid crystal display devices (LCDs) or general lighting.
An epoxy resin including an acid anhydride-based curing agent and thus having a high adhesive property and excellent dynamic durability has been widely used as an LED encapsulation material. However, the epoxy resin has problems in that it has low transmittance with respect to light ranging from blue to UV wavelength ranges and also shows poor light resistance. Accordingly, for example, Patent Documents 1 to 3 disclose techniques proposed to solve the above-mentioned problems. However, the encapsulation materials as described in the above-mentioned patent documents have a problem in that they still show poor light resistance.
Meanwhile, a silicone resin has been known as a material having excellent light resistance at a low wavelength range. However, the silicone resin has problems in that it shows low heat resistance and has a sticky surface after a curing process. To effectively employ the silicone resin as an encapsulation material for LEDs, it is necessary to ensure the characteristics such as a high-refractive index characteristic, crack resistance, surface hardness, adhesive strength and thermal shock resistance.